Images and video of the crash showed the plane on fire, with smoke billowing from the crumpled fuselage, lying on its belly on scrub grass at the airport. It had lost its tail.

The plane was Flight 214 from Seoul, South Korea, a spokesman for the F.A.A., Lynn Lunsford, said.

Firefighters were on the scene, but there were no immediate reports of the extent of casualties. It was not clear how many people had been on board.

David Eun, who said in a Twitter message that he had been a passenger on the plane, posted a picture of a downed Asiana jetliner from ground level, which showed some passengers walking away from the aircraft.

An aviation official, who did not want to be identified discussing a fluid situation, said that the plane was not making an emergency landing, and that the situation had been entirely normal until the crash. The cause was also unclear.

Stefanie Turner, who posted on Twitter that she had witnessed the crash, said that the “plane came in at a bad angle, flipped, exploded.”

Juan Gonzalez, the supervising manager at Amoura Café in the airport, said that he did not hear any explosions but was told by airport workers that the tail had snapped off when it landed.

“Right now, there is just a lot of smoke and all the fire trucks are trying to get to the plane,” Mr. Gonzalez said

There was no immediate answer at a number listed for Asiana at San Francisco’s airport.

What are your thoughts CLICK HERE to leave us a "QUESTION OF THE DAY” comment.

Want to be in the know for the next weather event, the next school closing or the next big breaking news story?

TextCaster alerts from 21Alive.com are your defining source for instant information delivered right to your cell phone and email. It's free, easy and instant. Sign-Up Now!Powered by Summit City Chevrolet